A substantial number of graphic recording systems have been developed to provide automated or computer controlled graphic recording upon a media. While the individual structures of such graphic recorders vary substantially, generally all include a media transport system in which the media is moved in a first direction and a moveable pen carriage which is supported and controlled to provide motion of the pen carriage in a second direction relative to the media motion. In most instances, the directions of media movement and pen carriage movement are orthogonal.
While a number of different graphic recording systems have been developed, generally, all comprise a rigid track structure supported above the media and aligned with the desired carriage path. The pen carriage supports a plurality of wheels or rollers configured to engage the track structure and facilitate the free motion of the pen carriage along the pen carriage path. A carriage drive system generally comprises one or more drive pulleys supporting a closed loop carriage band such that a portion of the carriage band is generally parallel to the track arrangement. A computer controlled motor drive system imparts precise motion to the carriage band. The pen carriage is coupled to the carriage band and is moved upon the track system in accordance with carriage band motion. The pen carriage must securely engage the track system and maintain a secure engagement while providing free motion along the carriage path. To meet these requirements, a number of carriage suspension systems have been developed. Generally, such systems provide a spring support system operative upon several of the carriage wheels to apply a predetermined securing force between the track structure and the carriage wheels or rollers. In other systems, the carriage is supported by rollers which fit within recessed grooves in the track structure and are captivated upon the track structure by the grooves.
In addition to the need to provide a secure engagement between the pen carriage and the track structure, it is also desirable to configure the pen carriage suspension system to accommodate the minor variations and irregularities found in even the most precise track structures. It is particularly important that the pen carriage maintain the appropriate angular relationship with the media to ensure that an accurate quality graphic recording image is produced. For example, angular changes or tilt of the pen carriage produces a corresponding tilt of the recording pen contact point with the media. Such tilt of the point of pen contact in turn produces image lines which are displaced from the intended position and may be crooked or waved or inconsistent in different directions.
Beyond the need for maintaining carriage angle, there arises a need to configure the carriage suspension system to respond quickly to minor track variations because of the carriage speed and the reciprocating character of carriage motion. At high speeds and reciprocating motion, uncompensated minor track variations produce a type of rattle in the carriage. This rattle can further degrade the quality of image produced upon the media.
There remains therefore, a need in the art for a system of pen carriage suspension for graphic recorders in which the pen carriage is securely engaged with the track structure and in which the appropriate captivating force is applied between the pen carriage and the track structure while providing free movement of the pen carriage upon the track. There is a further need for a pen carriage suspension system for graphic recorders which accommodates minor variations in the track structure while maintaining both the captivating force and the alignment of the pen carriage. There remains a further need for a system which responds quickly to the minor variation in the track structure to prevent carriage rattle.